THE

VEGETATION

OF

KARACHI

*

(with 5 figures, i~ photographs and i table) by IKRAM ILAHI CHAUDHRI (Department of Botany, University of Sind, Hyderabad, West Pakistan) Greater Karachi having an area of about 566 square miles is a subtropical maritime desert on the Arabian Sea (fig. i). It can be divided into three physiographic divisions namely, (a) the hilly areas having a maximum height of about 580 feet, (b) the lower alluvial valleys of the Hub, the Lyari and the Malir rivers, (c) the coastal areas consisting of mud or sand swamps in the south. The hills are mostly made up of white or pale coloured limestone and are bare of any soil except in crevices and depressions. The soil between the hills is alluvial in nature and has been deposited by the Hub, the Lyari and the Malir rivers. It is made up of sand and clay. The various areas have different proportions of these and consequently the consistency and porosity of the soil vary considerably. On the whole the soil is sandy and porous. Along the gradually sloping sea shore as well as in the interior are found sand dunes formed by the sand blown from the coast. The water table at certain places particularly near the sea shore is at 0. 5 foot depth and thus many places near the coast are swampy. The subsoil water is saline except in the dried river beds. The soil of Karachi on the whole are highly saline due to the nearness of the sea and often during the dry period of the year white incrustations appear on the surface. So far no account of the vegetation covering the whole region has been published. The vegetation of coastal sand dunes of Karachi has been dealt by CHAUDHR* and QADm (I958). Besides this some useful information on the plant life of this region exists in the paper by B•ATTER et al 0929). CLIMATIC C O N D I T I O N S The meteorological data discussed here have been taken from the climatological tables of observatories published by the India Government 0955)a - Rainfall

The average monthly rainfall at Karachi is shown in Fig. 2. The detailed analysis of the rainfall at Karachi has been carried out by NAQVI 0956). The average annual rainfall is 7.75 inches, out of which 6.i6 inches is received during the monsoon period from June to September. In rest of the months average monthly rainfall remains below o.so inch. NAQVI has shown that not only the rainfall at Karachi is of small amount but is also very variable. According to him during the ~oo years from I856 to t955 the actual annual rainfall had been higher than io inches on as many as 24 occasions and the highest annual rainfall during this period was zS.o inches in the year i869 and on three occasions the annual rainfall

* Received for publication i5.V.i96o.

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THE VEGETATION OF KARACHI

231

had been less than i.o inch. These great fluctuations in the rainfall make plant life very difficult and highly specialised.

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Fig. 2. Monthly average rainfall (A) and rainy days (B) at Manora, Karachi.

The mean annual number of days with o.io inch or more rainfall is 9.0 but the number of days with drizzle is much higher. Thus in this region it is not the total amount of rainfall but it is the nature of the rainfall that matters. Due to the absence of much rain in Autumn, Winter and Spring for a continuous period of about 8 months the perennial vegetation is forced into resting period in localities where ground water is not available. As far as the annual vegetation is concerned the winter annuals are absent from this region but in years of good rainfall during the monsoon period most of the area is covered with numerous summer annuals. As water is the main limiting factor for the existence of various species in this arid region the year may be divided into the rainy season lasting from June to September and dry season lasting from October to May for a continuous period of 8 months.

b -

Temperature

The monthly average minimum and maximum temperatures for Manora and Civil Air Port, Drig Road, are shown in Fig. 3 and 4. The temperature fluctuations show that areas close to the sea have a maritime trend but inland places record a continental character. Manora which is close to sea shows less range of diurnal temperature as compared to the civil airport meteorological station at Drig Road. The daily range of temperature at Manora is more than 19~ F in the three winter months of November, December, and January. It decreases rapidly from February to May with rise of humidity. During the monsoon period from middle of Jnue to middle of September it gets reduced to about 8~ F only. At civil Airport

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Fig. 3.

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Monthly average maximum (B) and m i n i m u m (A) Temperatures at Manora, Karachi, I00

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Fig. 4. Monthly maximum (B) and minimum (A) temperatures at Air Port, Drig Road, Karachi. the daily range is as high as 27 ~ to 30 ~ F during the period from October to March due to its continental character. The hottest month is May and coldest January. The whole area is free from frost and as a result many plants are not killed back to the ground during the winter months and attain abnormal sizes. For example Ca]ofr@isprocera BR., plant becomes tree in this region as compared to shruby growth in the northern parts of the West Pakistan Plains. c - Wind

The average monthly wind speed and direction are given in table I. Suspended thick dust or sand particles are a common phenomenon in Karachi. This along with strong winds characteristic of this region plays very important role in formation of sand dunes and succession of

THE V E G E T A T I O N O F KARACHI

z33

vegetation. The w i n d blows mostly from South West or W e s t w a r d directions and constantly carries sand and salt particles from the beach to the hinterland. H o w e v e r , during the winter months from N o v e m b e r to

Table I.

Mean monthly wind direction and speed in miles per hour in the morning (A.M.) and afternoon (P.M.) at Manora: Karachi Time

i. Mean wind speed

(a) Morning (b) Afternoon

z. Dominant wind

(a) Morning (b) Afternoon Time

t. Mean wind speed

(a) Morning (b) Afternoon

z. Dominant wind

(a) Morning (b) Afternoon

Jan. 6.a 9

Feb. IMarch I April I May 6.8 IO

8.z I4

9.7 x5

II.6 I6

June iz. 7 I8

NNE NNE W WSW WSW WSW SW WSW WSW WSW WSW W July

Aug.

Sep.

zz.8 17

ii. 9 I5

io.o I3

/Oct [Nov. 6.6 II

5-3 Io

Dec. 5.9 4

WSW WSW WSW W N N E NNE W WSW WSW WSW WSW WS

F e b r u a r y the w i n d often blows from land to the sea from N o r t h and N o r t h East directions and this being in the opposite direction it tends to reverse the process o f dune f o r m a t i o n to some extent. The crowns o f the trees in this region are oriented to the d o m i n a n t w i n d direction (photo i & I I).

Photo i.

Showing the wind effect on the growth of Tamarindus indica L. at Manghupir, Karachi.

234

I . I . CHAUDHRI

The wheat and other cereal crops are not very successful as due to strong hot winds the grains are very much shrivelled. d - Relative h u m i d i t y The data for relative humidity as observed at Manora and Air Port Drig Road is given in fig. 5. The percentage of relative humidity at Karachi is high. At Manora in the morning it ranges from 63 to 9~ and in the afternoon from 44 to 76 throughout the year. However it progressively decreases towards the interior as the distance increases from the sea. For example at Drig Road in the morning it varies from 49 to 78 and in the afternoon from 3I to 73 in different parts of the year. lO0

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Fig. 5. Percentage of monthly average relative Humidity at Manora (B) and Air Port, Drig Road (A), Karachi. During the period of April to October it is above 80 at Manora in the morning and from November to April it ranges from 63 to 79. Low relative humidity from November to April coupled with negligible winter rainfall makes plant life very difficult in this area and acts as a main factor in wgeding out many species from this area. Coupled with high relative humidity is the phenomenon of dew formation which plays a very important role in supplying the much needed water to the plants during difficult times. The data for dew formation in this area are not available. Some plants of this region like Tamarix troupii HOLE, Tamarix dioica Rox~., Sporobolus marginatus HO'CHST, Avicennia alba BLUM~, Urochondra setulosa (TRIN) C. E. Hm3t3, and Statice ,tocksii BoIss., excrete hygroscopic salts which have the capacity of absorbing water from atmosphere and are thus able to replenish their water supply during the night and colder parts of the day when the relative humidity in the atmosphere is high. COASTAL V E G E T A T I O N Along the Karachi coast three main types of associations are met with. In the protected creeks on the mouth of the rivers in shallow waters is found mangrove vegetation. On the gradually sloping sea shore away from the river or stream beds, particularly in the regions of Clifton and

THE VEGETATION OF KARACHI

235

Sandspits, are found sand dunes away from the tidal waves with their characteristic vegetation. In low lying water-logged regions all along the coast are met swamp plants. I -

Mangrove

In the protected creeks or the mouth of the rivers in shallow sea

Avicennia a]ba BLl~ae grows pure (Photo 2). The characteristic features

Photo z.

Mangrove vegetation consisting of pure growth of Avicem~ia alba BLUME.

of this plant are pneumatophores, excretion of salts from the leaves, vivipary and xerophytic characters due to the physiological drought. The germination of the seeds takes place during the monsoon period. The primary root soon dies and the adventitious roots take over. These plants are heavily lopped due to the scarcity of other fodders in the Karachi region and on account of this the size remains small. Few plants of Aegiceras majus GALRTN. are also found in this region. From the Indus delta region BLaTT~R et al (1929) have recorded Aegiceras majus GA~STN., Rhizophora mucronata LAM, Rhizophora conjugata L., Ceriops candolleana ARN, Ceriops roxburghiana ARN, Bruguiera gymnorhiza , Sonneratia acida L. and

Avicennia offlcinalis L. 2 -

Vegetation

of swamps

On the sea coast in the muddy water-logged areas Arthrocnemum indicum MOQ grows pure (Photo 3)- Further away from sea other plants like Tamarix troupii HoL~, Suaeda monoica FORSK, Prosojoisjuliflora Dc., Suaeda fruticosa FORSK, and t-Taloxylon recurvum BUNGE are found.

a36

Photo 3"

Photo 4.

I . I . CHAUDHRI

Pure growth of Athrocnemum indicum MOQ in the coastal swamp.

Pioneer stage Vegetation of coastal sand dunes consisting of Iara]opyrum macronatum (L) STaPF and Suaeda monoica FORSK.

THE VEGETATION OF KARACHI 3 -- S a n d d u n e s

237

Vegetation

All along the coast are found sand dunes on gradually sloping sea shore away from the river or stream beds and these coastal dunes are particularly met with in the regions of Clifton and Sandspit. The height of these dunes reach upto 4 ~ feet above sea level. The development of the dunes starts along the sea shore when the pioneer members of the dunes vegetation like Suaeda monoica FORSK, Suaeda nudiflora MOQ, Arthracnemum indicum Moq, Halopyrum mucronatum (L) STAPF, CyJoerus effusus ROTH, Aeluropsus ]agopoides (L) TRIx and Cressa cretica L. collect sand around them (Photo 4). The wind velocity being strong in this region the sand mostly gets deposited around plants on the opposite side of the wind. Such embryo dunes colonised by these pioneer plants are met with along the sea shore near to the mangrove vegetation and the plants are well adapte,d to saline swampy conditions. Further away from the sea the dune size increases and among the important plants which take part in this intermediate stage of dune development may be mentioned [pomaea pes-ca~rae RoT~, Cyperus arenarius R~TZ, Cit,wllus colocynthis SCHaD~R, Zepatadenia spartium WIGUT, Heliotropium currasadcum L., Launaea chondrilloidesHk.f, Atriplex stockdi BoIss., Salsola foetida DeL, and Aerva pseudotomentosa BLaTT & HALL, in addition to some members of the pioneer stage (Photo 5)-

Photo 5.

Vegetation of central part of the coastal dunes consisting of Ijoomaea

pes-caprae ROTH & Aerva pseudotomentosa BLATT & HALL.

On the largest dunes away from the sea Ca/otropis procera BR. and Tamarix troupii HoLe, are generally f o u n d (Photo 6 & 7). In some cases small trees of Prosopisju]iflora Dc, which is an exotic species from America are

238

I.I. CHAUDHRI

P h o t o 6.

Tamarix troupii HoLe occupying the highest dunes away from the sea, derva pseudotomentosa BLATr & HaLL can be seen at the base of the dunes.

P h o t o 7.

Large Calotropis procera BR. occupying a large sand dune, Cistanche lubulosa WIGHT appear in large n u m b e r o n these plants as root parasite.

THE VEGETATION OF KARACHI

239

also found in the area occupying some large dunes. The tree species characteristic of similar dunes at other places are absent from this region most probably due to biotic factors. V E G E T A T I O N OF CALCARIOUS ROCKS Throughout the area are found calcarious low hills not exceeding 580 feet in height. These hills are of marine origin and were most probably raised into dry land sometime during the Pleistocene. These rocks are devoid of any top soil due to soil erosion. A typical flora associated with calcarious soil is found in this area (Photo 8). The plants with the exception of few lichens, mosses and Riccia raflqii FARuQI and CI-IAUDHe,I, grow in the crevices. The pioneer vegetation consists of perennial herbaceous

Photo 8. A general view of the vegetation of the calcarious rocks. plants like Inula grantioides Bolss., Cleome viscosa L., Chloris inflata LINK, Fagonia cretica L., Viola stocksii Bolss., Enne@ogon persicum Bolss. and Lasiurus hirsutus (FoRsK) Bolss. These are succeeded by shruby plants of Commiphora mukul ENGL., Grewia villosa WILED., Grewia renan (FoRsK) ASHERS and SCHWEINF.,Cordia rothii R & S, Rhus m)'sorensis H1~YNE.,under the protection of some of the above mentioned shrubs Euphorbia caudicifolia HAIXES seedlings generally make their appearance (Photo 9)" Ultimately these seedlings develop into clumps upto Io feet in diameter and suppress the growth of the shrubs which had given them protection at the early stage of their development. Associated with these Euphorbia dumps are large number of climbers such as JEphedrafoliata Borss., I~ cynanchoides R.BR, Daemia extensa BR., Oxystelma esculantum BR., Cocculuspendulus DelLS, Rhynchosia arernaria BLATT and HALL, Latipes senegalensis KUNrH,

240

Photo 9.

I.I. CHAUDHRI

First stage of succession where Euphorbia caudicifolia HAINESseedling is growing under the protection of Commiphora mukul ENGL.

Ochradenus baccatus DeLILe, and other secondary species like Solanum gradlipes DcNe, Peristrophe bicalyculata NEes, Barleria acanthoides VAHL, and @mbopogenjwarancusa (JoNEs) SCHULT. MOSt of these species seem to flourish only under the microclimatic conditions created by Euphorbia caudidfolia HAINES clumps, tn due course of time in these clumps Acacia senegal WIELD. seedlings appear (Photo io) and ultimately dominate over the Eup/~orbia caudicifolia HAINES (Photo ii). The plants of these hills show great drought enduring properties. Due to the great yearly fluctuations in the rainfall the seedlings of various plants are able to survive only during the years of good rainfall. The plants are faced with drought conditions for a continuous period of eight months from October to May. During this period most plants pass into resting period and plants like Euphorbia caudicifolia HAINES, Grewia villosa WILLD., Grewia Tenax (FORSK) ASHeRS, Commiphora mukul ENGL., _Rhus mysorensis HerrNes shed their leaves during this dry period. The cuttings of Commiphora mukul ENGL. brought in November in the laboratory not only remained alive without any supply of water but started flowering and rooting at the end of May after being subjected to 7 months dry period without any supply of water. Another remarkable case of drought enduring properties of the vegetation of this region was discovered in case of Riccia rafiqii FARUQI and CHaUDHRI which was found to grow on the rocks of Monghupir hills. The drought resistance in this species was investigated by FaRUQI and CI-IAUDHRI(1960). The plants were found to revive on supplying them water after keeping them dry in a bottle under ordinary laboratory conditions for over two years.

THE VEGETATION

OF KARACHI

z4i

P h o t o IO.

Second stage of succession where Acacia senegal WILLD, has started g r o w i n g in the clump o f t~uphorbia caudicifolia HAINES.

P h o t o I I,

Acacia seJ~egalWILLD. forest near G a h r o showing the effect of strong coastal wind currents.

Vegetatio, X, 5-4.

x6

242

I.I. CHAUDHRI V E G E T A T I O N OF T H E ALLUVIAL AREAS

In the valleys between the hills alluvial soil has been deposited over the basic rocks. These valleys are sloping and are drained by stream or rivers which flow for a short time after the rains. In these valleys typical climatic climax vegetation consisting of ProsodOis spicigera L. and Salvadora oleoides DcN~ form fixed dunes (Photo ia). The top soil is saline consisting of

Photo xz.

The climax vegetation consisting of Prosopis sp#igera L. and Salvadora oleoides DcNE, forming fixed dunes in the alluvial valleys near Ban Murad.

mainly Sodium salts which appear at the top in the form of white incrustations during dry months. Due to high concentration of the salts in the top soil the pioneer vegetation consists of halophytic perennial herbs like Sporobolus marginatus HocI~s% Suaeda fruticosa FORSK, Corchorus depressus STOCKS, Eupaorbiagranulata FORSK, Convolvulus pluricaulis C~oIs, Farsetia jacquemontii H.f and T, Amberboa divaricata (DC) O. KuNTze, Boerhaavia diffusa L. and Tribulus alatus DEI, The aerial parts die during the dry period but root stumps survive to grow again in the rainy season. Small quantities of blown soil get deposited around these plants and ultimately in such improved places due to leaching of salts by rain and addition of humus Capparis decidua (FORSK) EDCEW, Lycium europeum L. shrubs make their appearance. These shrubs in return are ultimately replaced by Salvadora oleoides DcNe and Prosopis spicigera L. These dunes are often inhabited by secondary species like Eleusine flagellifera N•es, Cenchrus pennisetiformis HOCHST, Cenchrus biflorus Rox~., Solanum gradlipes

THE VEGETATION OF KARACHI

243

DCN~, along with climbers such as Cocculuspendulus (FoRsT) Dmns, Cocculus hirsutus D~Its, E~hedra foliata BoIss., Pentafropis spiralis DCNt~, and Momordica dioica ROXB. The layer of alluvium being thin in the depressions the soil gets highly saline and waterlogged. Such areas are colonised by Urochondra setulose (TRIN) C.E. Hu~3B, Suaeda fruticosa FORSK and Aelurosus lagopoides (L) TRiN (Photo 13). In such areas ultimately fixed dunes of Salvadora persica

Photo 13.

Suaedafruticosa FORSK and Urochondra setulosa (TRIN) C. E. Hu~B growing in the highly saline soil in the depression.

L. appear. In comparatively less saline depression patches of Acacia arabica WILED. are found throughout the region. In the dried river beds the common species are Tamarix troupii HOLL, Tamarix dioica Roxl3., and Nerium odorum SOLAND. In the ponds and ditches the usual water vegetation of this region consisting of Typha angustata CHaUB & BORY, Phragmites karka TRIN, Ipomea aquatica FORSK,Nelumbium nucifera GAERTN. are found. Near Manghupir are met hot water sulphur springs and in this oasis date palm groves are dominant (Photo I4). Besides date palm, Ricinus communis L. and some vegetables are also commonly grown. Euphorbia triucalli L. is commonly grown as shelter belt around the cultivated areas. In the Malir area where sweet subsoil water is available in the river alluvium usual crops are grown b y tube well irrigation. The common fruits plants are Mangifera indica L., Phoenix dactylifera L., Carica j~ajgayaL., Cocos nucifera L., Psidium guyava L., Zizyjohusjujuba LAMB and Musa sapientum L. In the Ban Murad area irrigation is carried out from the Hub river i6"

244

I . I . CHAUDHRI

Photo 14.

An oasis of Phoenix daclylifera L. where spring water is available in the valley near Manghupir for irrigation.

Photo 15.

The vegetation of the catchment areas in the valleys where rain water is collected by constructing bunds, The upper dry end is dominated by Suaeda frulicosa, FORSK. In the middle is Cassia angustifolia VAHL and moist lower end is colonized by Indigofera obJongifolia FORSK, and Dicanthium annulatum (FoRsK) STAVF.

THE VEGETATION OF KARACHI

245

and usual crops of the area are grown. In the city of Karachi in gardens, Parks and road sides large number of exotic plants are found. Dry farming is carried out throughout the valleys in areas with gradual slope by constructing 'bunds' to collect the rain water (Photo I5). At such places along the slope generally definite zonation of vegetation can be observed in the catchment area depending on the amount of water in the soil. At highest level are found halophytic species like Suaedafruticosa FORSK, Cressa cre/ica L., Fagonia cretica L. and S~orobolus margina/us HocI4sT. In the middle portion are found Eleusine flagellifera NEEs, Eleusine aegyp/ica Dt~sF, Sesbania sesban (L) MIP,R~LL, Cenchrus biflorus ROXB., Senera incana CAr, and Cassia angustifolia VAHL, and at the lower moist end Dicanthium annulatum (FORSK) S:rApi~ and [ndigeofera oblongifolia FORSK. Towards the lower moist end crop like Pennise/um typhoides (BuRM) S t a f f et Hum3, Sorghum vulgare PERS., Cajanus indicus SPReNG, Cyamopsis tetragonoloba (L) TAUB, Sesamum indicum DC and Pisum sativa L. are grown successfully. CONCLUDING REMARKS The climax vegetation of the region consists of Salvadora o/eoides DcNir and JProsopis spicigera L., which are restricted to the alluvial soils of the valleys. The vegetation of the rocks is replaced gradually by the above mentioned species when enough soil has been deposited on the basic rocks. With the receding of the sea and deposition of the alluvium the coastal vegetation is also giving way to the plants characteristic of alluvial soils. The elements of coastal vegetation are predominantly tropical and are mostly related to the Indo-Malayan region. The plants of the calcarious rocks are very drought resistant and are dominated by the Afro-Asian desert element. The dominant plants of the alluvial soil are mostly indigenous to the Indo-Pakistan subcontinent. BLaTT~R et al (I9z9) have shown that on the whole Indus delta has more western elements than the Sunderban in East Pakistan. The different plants of this region mostly belong to the categories of summer annuals, perennial herbaceous, shrubs and trees. The winter annuals and biennials are mostly absent from this area due to unfavourable climatic conditions. The summer annuals germinate in June and dry up by October. The perennial herbaceous plants start growth in spring, die back to the ground by November and remain underground during the winter. Such plants have to face very unfavourale conditions of moisture and thus have very well developed root system besides succulent thick leaves. The shrubs and the trees of the rocks like Acacia senegal WrLnD., Euphorbia caudicifolia HaiNes, Commi/ohora mukul ExGI~., Grewia /enax (FoRsK) BoIss., Grewia villosa WILLD. are faced with drought conditions for a continous period of 8 months from October to June and most of this period they pass in leafless dormant condition. The majority of the trees and shrubs of the alluvial soil and coastal regions are evergreen and generally flower twice in a year during spring and autumn. Summary The vegetation of Greater Karachi can be divided into three edapbic types.

246

I . I . CHAUDHRI

The coastal vegetation consists of three main associations. In the protected creeks facing the mouth of the rivers in shallow water is found mangrove vegetation consisting of mainly Avicennia alba BLI~ME. In the muddy coastal swamps Arthroenemum indicum MOQ is the main species. On the coastal sand dunes the main species consist of Suaeda monoica FoRsK, Ipomaea pes-caprae ROTH, Aerua pseudo-tomentosa BLATT and HALL, Calotropis procera Be,. and Tamarix troupii, HOLE~ The vegetation of the calcarious rocks consists of mainly Commiphora mukul ENGL., Grewia villosa WILLI)., Grewia tenax (Foe,sK) Bolss., Euphorbia caudicifolia HAINES and Acacia senegal WILLD. In the valleys between the hills where alluvium has been deposited over the basic rock by various rivers, the vegetation consists of Capparis decidua (FoRsK) EDGEW, Prosopis spicigera L. and Salvadora oleoidesDCNE. Rdsumd

La vdg&ation de la rdgion de Karachi peut 4tre divisde en trois types trhs difffrents au point de vue 6daphique. La vdg&ation littorale se compose de trois associations principales. Dans les criques protdgdes, en face des embouchures des fleuves, la v6g&ation de la mangrove s'avance dans l'eau peu profonde. Elle consiste principalement d'Avicennia alba BLUME. Darts les marais tourbeux du littoral, Arthrocnemum indicum MOQ. occupe la premihre place. Sur les dunes littorales, les esp~ces principales sont Suaeda monoica FORSK, Ipomaea pes-caprae ROTH., Aerua pseudo- tomentosa BLATT et HALL, Calotropis procera BR. et Tamarix troupii HOLE. La vdgdtation des rochers calcaires se compose principalement de

Commiphora mukul ENGL., Grewia villosa WILLD., Grewia tenax (FoRsK) BOlSS., Euphorbia caudicifolia HAINES et Acacia senegal WILLD. Sur les alluvions des fleuves on note une vdgdtation comprenant Capparis decidua (FoRsK) EDCEW, Prosopis spicigera L. et Salvadora oleoides DCNE. La vdg6tation climax de la rdgion est dominde par Salvadora oleoides DCNE et Prosopis spicigera L. REFERENCES

BLATTER,E., C. McCANN and T. S. SABNIS,1929 - Flora of the Indus Delta. Madras.

CHAUDHRI,I. I. and S. A. QADIR, 1958 --Vegetation of the Sand Dunes of Coastal regions of Karachi. Pak. J. Forestry, 8, 4, 337-341. FARUQI, B. A. and I. I. CHAUDHRI,196o - Droughtand Heat resistance in R#cia rafiqii, F. & C. Pak. ar. sd. Res. iz, 3 I25-I29. NAQVI, S. N., I956 - Periodic variations in water balance in an arid Region: A preliminary study of ioo years rainfall at Karachi. Proc. UNESCO Syrup. on Arid Zone Climatology with special reference to microclimatology. Canberra, Australia, October, 1956.